“Of the second order” is used when a concept is applied to one or several instances of the same concept:

In mathematics second order function is a function that operates on some functions and has a function as a result.
A language of the second order would be a language build on top of one or several languages (for example Pig Latin)
A joke of the second order would be a joke which is using another joke.

Meta bears the meaning of a concept applied to all instances of the same concept (all instances within the restraints of the concept, of course, not all in the Universum).

A “metalanguage” would be a language that can define any other language (this is known to the masses as “grammar” :)
A “metajoke” is a joke that encompasses all jokes.
A meta-”walk into a bar”-joke would be:

An Englishman, an Irishman, and a Scotsman walk into a bar.
The bartender turns to them, takes one look, and says “What is this - some kind of a joke?”

Of course in informal speech, everything goes as far as it makes you understood, and the fine distinction between ’some’ and ‘all’ is usually not important in everyday talks, except you’re a manic nitpick.